“Clarification” is the settling or removal of suspended solids from a liquid, for example in municipal water treatment, the treatment of sugar cane juice, or the manufacture of pulp and paper. Existing clarifier designs have the general disadvantage that large, turbulent eddies are created as liquid flows into the tanks. The turbulence results in inefficient use of the settling area, reduced quality of the liquid overflow, and generally imposes longer residence times than would otherwise be needed. A longer residence time is inherently less efficient and more expensive, especially where perishable or degradable products are involved. For example, in the clarifying sugar juice, a longer residence time can result in partial product deterioration.
Clarification of sugar cane juice is an important part of the milling process. A standard design employs a cylindrical tank with a sloped base, with or without a raking mechanism to remove sludge. Clarified liquid is removed through overflow launders, typically positioned on the periphery of the tank. Alternatively, in a rectangular device, the feed inlet is located on the side opposite from the overflow launder. Some clarifiers include a central well for dispersing flocculants. In most conventional clarifiers, liquid travels horizontally outwards and vertically upward, following a path from the central feed well to overflow outlets or launders (the so-called Dorr design), or from the periphery to a central outlet (the so-called Graver design). The horizontal flow reduces efficiency and throughput: It creates a large-scale, circular motion inside the clarifier, which decreases performance and separation efficiency. A separation that takes only a few minutes on a small scale can take from 30 minutes to several hours in a mill due to the effects of turbulence on settling time.
Both computer modeling and experimental visualization have demonstrated that most existing clarifier designs are inefficient, and are subject to large-scale turbulence. These inefficiencies lead to increased production costs, lower quality output, or both.
Some prior clarifier designs have employed multiple plates to increase settling area and to reduce eddies, but these designs have typically been too expensive and complex for widespread commercial use.
In other prior designs the inlet flow enters the clarifier either through distribution trays or feed launders that provide a large surface area to slow fluid flow. Even so, large-scale eddies can still be created in these devices due to the large mass of flow entering the clarifier. Other design alternatives have not been widely accepted in the sugar industry.
Some recent clarifier designs are more efficient, with reduced residence times. However, these newer designs are more expensive; their installation would require most mills to purchase new equipment or to pay for costly re-engineering. Also the hydrodynamic conditions in the new designs, while somewhat improved, are not much different from those in conventional designs. They typically produce lateral flows that can create large eddies that interfere with settling.
A “lamella” type clarifier uses a stack of parallel, inclined plates within a rectangular vessel to shorten sedimentation pathways. Significant additional surface area is provided for settling, and the travel distance for liquid is reduced. Significant issues for a lamella clarifier include the removal of solids and cleaning of the lamellae. The cost for a lamella clarifier can be significant, especially if it is constructed from a non-polymeric material. (Polymers can be difficult to use with high temperature sugar solutions.)
U.S. Pat. No. 2,488,851 discloses a sugar juice clarifier with a plurality of superposed settling trays.
U.S. Pat. No. 2,470,076 discloses a so-called “Dorr” clarifier, similar to those that are commonly used in sugar mills today.
U.S. Pat. No. 2,611,685 discloses a reaction vessel for contacting vapors with fluidized, finely divided particles. A series of truncated, concentric cones is arranged in the bottom of the vessel to achieve even fluid distribution across the diameter of the reactor.
U.S. Pat. No. 4,609,010 discloses a fluid distribution system that employs a series of perforations in a fluid inlet distributor.
U.S. Pat. No. 5,192,465 discloses a distributor assembly comprising a distributor plate adapted for horizontal positioning and securement to a process column liquid distributor for the symmetrical discharge of liquid therefrom. The distributor plate comprises a member having side walls formed therearound and a plurality of apertures formed therein. The distributor plate is constructed for collecting liquid discharged from the liquid distributor, spreading the liquid thereacross and affording low velocity equal discharge of liquid therefrom into a packing bed therebeneath.
U.S. Pat. No. 3,556,736 discloses an apparatus for contacting two fluids in a fluid-solids contact zone.
U.S. Pat. No. 4,479,875 discloses an inlet distributor for liquid-liquid separators, in which fluid passes through a packing means to provide a pressure drop.
U.S. Pat. No. 4,780,206 discloses a turbulence control system comprising a first baffle, fixedly connected across the interior of an intra-channel clarifier having side walls between the side walls near the point of entry of wastewater into the clarifier, the first baffle covering a desired portion of the cross-sectional flow area within the clarifier; and a second baffle, fixedly connected across the interior of the clarifier between the side walls downstream of the first baffle and covering a desired portion of the cross-sectional flow area left uncovered by the first baffle. The turbulence control system may also comprise at least one accumulation baffle, connected between the side walls and near the bottom of the clarifier, the accumulation baffle extending upward to a desired height within the clarifier, but not so high as to produce a flow velocity that would impede settlement of sludge within the clarifier.
U.S. Pat. No. 5,378,378 discloses the use of helical inlet flow to reduce the energy of liquid and solids flowing in a basin toward a clarifier.
U.S. Pat. No. 5,354,460 discloses a step-down nozzle for the even distribution of fluids at the interface between phases in a column or cell accommodating a plug flow operation structured with an internal flow channel of recursive configuration.
Scott, R. P. (1988). Modification to and experiences with RAPIDORR clarifiers including saccharate liming at Amatikulu. Proc S Afr Sug Technol. Assoc. 62: 32-35 discloses a Dorr-type clarifier, which introduces feed through a hollow rotating pipe in the center of the clarifier. This device distributes the feed into several compartments within the clarifier, in each of which the flow is deflected by a baffle.
Steindl, R. J., Fitzmaurice, A. L. and Alman, C. W. (1998). Recent developments in clarifier design. Aust. Soc. Sugar Cane Technol., 20: 477-483 discloses the use of a single-point feed system to produce a constant velocity in the feed launder, and a uniform distribution of feed around the circumference of the feed well.
U.S. Pat. No. 5,938,333 discloses a fractal design to provide “geometric” control over flow to reduce turbulence.
U.S. Pat. No. 5,944,995 discloses a clarifier in which the feed well diameter increases from top to bottom in a conical shape to decrease the fluid velocity. It also incorporates baffles for added velocity reduction. The base of the feed well includes a downwardly and inwardly angled rim to further reduce velocity.
U.S. Pat. No. 6,800,209 discloses a device that incorporates equally-spaced ports around the circumference. Each port includes baffles that direct the feed stream tangentially, in opposite directions. Energy is dissipated when fluids from adjacent ports collide.
Prior work by the inventors has been presented as: V. Kochergin, C. Gaudet, M. Robert, S. Bergeron—Experience with new design of juice clarifier, ASSCT LA division, Lafayette, La. Feb. 2-3, 2010; and largely cumulative is the following presentation: V. Kochergin, and C. Gaudet, New Approach to Fluid Distribution in the Industrial Clarifiers—40th Joint Annual meeting of ASSCT Florida and Louisiana Divisions, Panama City Beach, Jun. 16-18, 2010. See also V. Kochergin, “A Juice Clarifier with Turbulence Reduction Devices,” Proceedings of South African Sugar Technologists' Association 83rd Annual Congress, Aug. 25-27, 2010, Durban, South Africa.